Compressible gas ejector with unexpanded motive gas-load gas interface

ABSTRACT

A compressible gas ejector is configured to present unexpanded motive gas to a load gas, wherein the interface of the unexpanded motive gas and the load gas can be located in a suction chamber or within a downstream diffuser. The ejector includes a motive funnel for increasing the velocity of a relatively high pressure motive gas, the motive funnel substantially precluding adiabatic expansion of the motive gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A “SEQUENCE LISTING”

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ejectors, and more particularly to acompressible gas ejector having an unexpanded motive gas exposed to aload gas, wherein the interface of the unexpanded motive gas and theload gas can be located in a suction chamber or a downstream diffuser.

2. Description of Related Art

Steam jet ejectors are employed in the chemical process industries,refineries as well as power generation plants, stills, vacuum deaeratorevaporators, crystallizers, steam vacuum refrigeration, flack coolers,condensers, vacuum pan dryers, dehydrators, vacuum impregnators, freezedryers and vacuum filters. The ejector provides a vacuum that can beapplied, depending upon the design of the ejector, from relatively smallloads to significant loads. Ejectors can also be used to evacuate airand/or combustion products in aerodynamic and combustion processes.

Ejectors can also be used to provide the vacuum (pressure belowatmospheric) for the production of natural fats and oils and derivativeoleochemicals. In addition, degumming, bleaching, interestification,fractionation, winterization and deodorization are often supported byejectors.

As seen in FIG. 1, a prior art ejector includes a motive venturi, asuction chamber and a downstream diffuser. The motive venturi includes aconverging section, a throat and a diverging section, wherein thesuction chamber encompasses (and is thus fluidly exposed to) the opendiverging end of the motive venturi. The suction chamber is fluidlyexposed to a suction inlet and hence to a load gas and the diffuser. Thediffuser is also a venturi and includes a converging section beginningin the suction chamber, a throat and a diverging section.

Generally, the ejector converts pressure energy, for example, a motivestream, into kinetic energy (velocity). Referring to FIG. 1, prior artsteam ejectors 1 obtain the desired by velocity by the adiabaticexpansion of the motive steam through a convergent and divergent sectionof the motive venture 3. As seen in FIG. 1, the velocity of the motivesteam continually increases as the motive steam passes along thedivergent section of the motive venturi. The motive steam is typicallyexpanded to the pressure of the load gas. The high velocity motive steamthen passes into a suction chamber 5. The resulting high velocity,motive steam is then retarded in the suction chambers while the loadsteam is accelerated in the suction chamber and forms a mixture.

The mixture passes through the converging section, the throat and thediverging section of a diffuser 7, wherein the high velocity isconverted back into pressure. Thus, the mixture can be vented toatmospheric pressure, or additional ejectors can be employed tosufficiently raise the pressure to atmospheric pressure.

In certain applications, it is advantageous for the ejector to remove acertain ratio of motive gas to load gas. Historically, in sub criticalflows, the ejectors are only able to provide a motive mass flow to loadmass flow ratio of approximately 2.0. However, certain applications canbe provided with increased efficiency, if the ratio of motive mass flowto load mass flow is on the order of 1.5. Therefore, the need exists fora compressible gas ejector that can reduce the ratio of motive gas massflow to load gas mass flow.

BRIEF SUMMARY OF THE INVENTION

The present ejector provides a compressible gas ejector with an improvedmotive gas mass flow to load mass gas flow ratio.

In one configuration, the present compressible gas ejector provides forthe direct contact of unexpanded motive gas with the load gas. Dependingupon the particular construction, the interface between the unexpandedmotive gas and the load gas can be located in the suction chamber or aconverging section of the diffuser.

Contrary to prior teachings which suggest detrimental instability uponexposing unexpanded motive flow in the suction chamber, the presentconfiguration provides stable mass flow rates, with the unexpandedmotive gas directly mixing with the load gas.

In a further configuration, the compressible gas ejector, includes aconverging motive funnel, the motive funnel having a converging sectionbeing substantially free of a downstream diverging section; a suctionchamber fluidly connected to the motive funnel; and a diffuserdownstream of the suction chamber, the diffuser including a convergingsection and a downstream diverging section. In one configuration, adownstream end of the motive funnel is disposed within the convergingsection of the diffuser.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a cross-sectional view of a prior art steam ejector.

FIG. 2 is a cross-sectional view of the present ejector.

FIG. 3 is a cross sectional view of a regulator for controlling flowthrough the motive funnel.

FIG. 4 is a cross sectional view of an alternative regulator.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, the present compressible gas ejector 10 is shown.For purposes of description, a motive gas 12 is introduced into theejector to draw a load gas 14 into the ejector so as to form a mixture16, wherein the mixture exits the ejector 10 at a downstream location.The term “motive gas” 12 is intended to encompass any of a variety ofmotive flows including steam, vapor or other compressible flows, as wellas mixtures thereof. The term “load gas” 14 is intended to encompass anyof a variety of load gases such as, but not limited to processby-products, combustion products or other compressible flows, ormixtures thereof.

The ejector 10 includes a suction chamber, an upstream motive funnel 20and a downstream diffuser 60, wherein the motive gas 12 passes throughthe motive funnel 20 and mixes with the load gas 14 from the suctionchamber and is discharged through the diffuser.

As seen in FIG. 2, the upstream motive funnel 20 and the downstreamdiffuser 60 extend along a longitudinal axis and are generally coaxial.As the suction chamber 40 encompasses a portion of the motive funnel 20and interfaces with the diffuser 60, the suction chamber also includes adimension extending along the longitudinal axis.

Therefore, for definitional purposes, a component or portion of themotive funnel 20 or the diffuser 60 can be described in terms of a“length” which is a dimension extending along the longitudinal axis. Awidth of a component is that dimension transverse to the longitudinalaxis.

The suction chamber 40 includes a suction inlet 42 fluidly connected tothe load gas 14, which is to be drawn into the ejector 10 and passedthrough the diffuser 60.

The converging motive funnel 20 is fluidly connected to a source of themotive gas such as steam from a turbine discharge. The motive funnel 20includes an entrance port 22 and a downstream exit port 24, wherein theentrance port is larger than the exit port. A converging section 26extends from the entrance port 22, and in selected configurations,terminates at the exit port 24. Thus, in contrast to prior ejectors, thepresent converging motive funnel 20 does not include a divergingportion, and thus presents unexpanded motive gas 12 to the load gas 14.

In other configurations, the motive funnel 20 can include a throat 30downstream of the converging section 26, wherein the throat defines asubstantially constant cross-section along the longitudinal axis andterminates at the exit port 24 of the motive funnel. Typically, thethroat 30 of the motive funnel 20 will have a length that is less thanthe length of the converging section 26 of the motive funnel. In thisconstruction, a downstream end of the throat 30 defines the exit port24, and hence the downstream end of the motive funnel 20.

The motive funnel 20 is selected to provide substantially unexpandedmotive gas 1 2 at the exit port 24. Thus, the particular convergencewithin the motive funnel 20 is at least partially determined by theintended operating parameters.

In one satisfactory configuration, the diameter of the entrance port 22can be between approximately 1.85 to 2.25 times the diameter of the exitport 24. The inlet diameter of the entrance port 22 of the convergingsection of the motive funnel 20 can be greater than the length of themotive funnel. Typical angles for the converging section of the motivefunnel 20 are between approximately 35° and approximately 80°, with atleast one satisfactory angle of approximately 60°.

It is understood the motive funnel 20, or the downstream end of thethroat 30, can include a de minimis diverging taper 32, such as along awall thickness of the funnel. That is, the exit port 24 can include adiverging flare on the order of less than 5% of the area of the exitport. However, such diverging taper 32 does not allow a materialexpansion of the motive gas.

In selected configurations as seen in FIG. 3, the motive funnel 20includes a regulator 34 to effectively reduce the cross sectional areaof the exit port 24 without changing pressure of the motive gas. Theregulator 34 thus provides for the selective reduction in the amount ofmotive gas 12 passing through the motive funnel 20. In oneconfiguration, the regulator 34 moves relative to the exit port 24 toeffectively change the cross sectional area of the exit port. Theregulator 34 is selected to substantially maintain the pressure dropalong the ejector 10, thereby maintaining efficiency of the ejector.

In one configuration of the regulator 34, the regulator includes agenerally tapered spike 36 which can be moved along the longitudinalaxis towards and away from the exit port 24 of the motive funnel 20.Referring to FIG. 3, the spike 36 can be curvilinear such as parabolic.In one configuration of the parabolic spike 36, the curvature is definedby the relation Y=√{square root over (0.008)}(x). In an alternativeconfiguration, the spike 36 defines a conical cross-section, as seen inFIG. 4.

The diffuser 60 includes a converging section 62, a throat 64 and adiverging section 68. The converging section 62 includes an inlet 61 anda downstream outlet 63 coincident with the throat 64. In contrast toprior ejectors, the present diffuser converging section 62 has a lengththat is less than an inlet diameter of the converging section. Incertain constructions, the inlet diameter of the converging section 62is on the order of twice the length of the converging section 62.Functionally, the diameter of the inlet 61 and the length of theconverging section 62 are selected to substantially maintain a steadystate operation of the ejector 10 at the intended flow rates.

It is further contemplated, that in selected configurations, thediameter of the inlet 61 of the converging section 62 is at least 1.5,and can be greater than twice the diameter of the outlet 63 (the throat64 of the diffuser 60). As the inlet diameter of the converging section62 increases, the interface area between the load gas 14 and theunexpanded motive gas 12 increases, with the downstream end of themotive funnel 20 remaining within the length of the converging sectionof the diffuser.

In certain constructions, the diverging section 66 of the diffuser 60 islonger than the converging section 62 of the diffuser, wherein thediverging section can be at least twice the length of the convergingsection.

As seen in FIG. 2, the exit port 24 of the motive funnel 20 is disposedwithin the inlet of the converging section 62 of the diffuser 60. Thatis, as the converging section 62 of the diffuser 60 extends along thelongitudinal dimension, the exit port 24 is located within the samelength of the longitudinal dimension. The amount of penetration of themotive funnel 20 into the converging section 62 of the diffuser 60 canrange from approximately 1% of the length of the converging section toapproximately 50% of the length of the converging section.

Therefore, a flow path of the motive gas 12 passes through the motivefunnel 20 and the exit port 24, to then enter the converging section 62of the diffuser 60. Load gas 14 is drawn in through the suction inlet 42and mixes with the motive gas 12 in the converging section 62 of thediffuser 60 to form the entrained mixture 16, wherein the entrainedmixture passes through the diffuser 60 and increases pressure.

It has been found advantageous to employ the present ejector 10 in a subcritical flow regime. That is, the pressure of the motive gas 12 is lessthan twice the pressure of the load gas 14.

Further, it has been found that the motive funnel 20 can discharge themotive gas 12 into the suction chamber 40, or the converging section 62of the diffuser 60 at a pressure that is lower than the load gas 14.

While the invention has been described in connection with a presentlypreferred embodiment thereof, those skilled in the art will recognizethat many modifications and changes may be made therein withoutdeparting from the true spirit and scope of the invention, whichaccordingly is intended to be defined solely by the appended claims.

1. A compressible gas ejector system, comprising: (a) a convergingmotive funnel, the motive funnel including a converging section andbeing substantially free of a downstream diverging section; (b) asuction chamber fluidly connected to the motive funnel; and (c) adiffuser downstream of the suction chamber, the diffuser including aconverging section and a downstream diverging section.
 2. The system ofclaim 1, wherein the motive funnel is selected to present substantiallyunexpanded motive gas to the suction chamber.
 3. The system of claim 1,wherein the motive funnel is selected to present substantiallyunexpanded motive gas to the diffuser.
 4. The system of claim 1, furthercomprising a load gas fluidly connected to the suction chamber, apressure of the load gas being greater than approximately one half apressure of the motive gas.
 5. The system of claim 1, wherein a pressureof a motive gas passing from the motive funnel is less than a pressureof a load gas in the suction chamber.
 6. A method of operating acompressible gas ejector, comprising: (a) expressing an unexpandedmotive gas into a converging section of a downstream diffuser to form anentrained flow.
 7. The method of claim 6, further comprising passing themotive gas through an upstream motive funnel and maintaining a pressureof the motive gas upstream of the motive funnel less than approximatelytwice a pressure of a load gas.
 8. The method of claim 6, furthercomprising providing a ratio of motive gas flow rate to a load gas flowrate of approximately 1.5 or less.
 9. A compressible gas ejector fluidlyconnected to a load gas, comprising: (a) a motive funnel consistingessentially of a converging portion and a throat to expose asubstantially unexpanded motive gas flow to the load gas.
 10. Theejector of claim 9, further comprising a downstream diffuser having aconverging section, the motive nozzle throat located within theconverging section of the diffuser.
 11. A compressible gas ejector,comprising: (a) a diffuser having a converging section and a downstreamdiverging section, the converging section having an inlet diametergreater than a length of the converging section.
 12. A method ofoperating a compressible gas ejector, comprising: (a) passing a flowmixture including a motive gas and a load gas through a diffuser, thediffuser having a converging section with an inlet diameter less than alength of the converging section.
 13. A compressible gas ejector forcompressing a load gas to a higher pressure, the ejector comprising: (a)a motive funnel having a converging portion and an exit port; and (b) adownstream diffuser having a converging section, the exit port locatedwithin the converging section.
 14. A compressible gas ejector,comprising: (a) a diffuser having a converging section, the convergingsection having an inlet; and (b) a motive funnel upstream of thediffuser, the motive funnel having an exit port sized to introduceunexpanded motive gas into the inlet.
 15. The ejector of claim 14,wherein the exit port is within the inlet.